Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Substances such as hair are hygroscopic and permeable, such that they can absorb moisture from the environment. For example, hair typically contains moisture accounting for about 12% to about 15% of the total weight. The hygroscopic property of hair determines the health of the hair, which can then determine available styling options for the hair. The capability of hair for retaining moisture can be deteriorated when it is damaged through styling such as a hair perm, exposure to hair styling products and exposure to hair dyes. Accordingly, it is important to precisely measure hair moisture to determine the overall health of hair or the moisture content in hair so that once can assess possible styling options and hair care options to maintain or improve the health of the hair.
Hair moisture measuring devices have been developed to detect the moisture level in hair, and have employed various techniques including a NIR (near infrared) moisture meter and Raman spectroscopy. The NIR moisture meter relies on the property of water that absorbs a specific wavelength of NIR light. However, it may be difficult to precisely measure the attenuation of the NIR light reflected from thin and fine hairs. Also, different levels of moisture at the surface and inner side of hair make the moisture measurement more challenging. The Raman spectroscopy relies on inelastic scattering of monochromatic light such as laser light irradiated on molecules of moisture in hair. For example, the laser light interacts with molecular vibrations, resulting in the energy of the laser photons being shifted upwards or downwards between a ground energy state and a virtual energy state. The shift in energy provides information about the vibrational modes to identify the molecules of moisture. Although the Raman spectroscopy provides decent precision of moisture measurement, it is costly and may not be implemented in a portable size for individual users.